Charge injection auxiliary material and organic electroluminescence device containing the same

ABSTRACT

A functional layer, such as a light emitting layer, of an organic electron device, such as an organic electroluminescence device, is provided. The function layer includes a small amount of a charge injection auxiliary material capable of enhancing charge injection properties. The charge injection auxiliary material comprises a stilbene, distyrylarylene or tris(styrylarylene) compound and is employed in an organic electron device wherein a positive-hole transporting organic functional layer is subjected to positive-hole injection from an external layer by incorporating the charge injection auxiliary material in the functional layer. The organic electroluminescence device provided by the present invention has a lowered applied voltage, an enhanced luminous efficiency and a prolonged service life.

TECHNICAL FIELD

The present invention relates to a novel charge injection auxiliarymaterial and an organic electroluminescence device containing the same.More particularly, it pertains to a charge injection auxiliary materialcapable of enhancing charge injecting properties which comprises aderivative of stilbene, distyrylarylene or tris(styrylarylene) and anorganic electroluminescence device having a lowered applied voltage, anenhanced light emission efficiency and a prolonged service life whichcontains the above-mentioned charge injection auxiliary material.

BACKGROUND ART

In recent years, it has been desired that an organic electronic devicesuch an electrophotographic photoreceptor, an organicelectroluminescence device (herein-after sometimes abbreviated to an"organic EL device"), organic transistor, an organic sensor and the likebe capable of stably and efficiently injecting an electric charge froman electrode or charge generating layer to a charge transporting layer.Examples of such devices capable of stably and efficiently injecting anelectric charge include a device comprising a positive-hole injectinglayer having carbon black dispersed therein which layer is interposedbetween a type-P photoconductor layer and a supporting substrate (referto Japanese Patent Application Laid-Open No. 12848/1984) and a deviceimproved in charge injecting properties which comprises two divisionalcharge transporting layers, whose layer on the side of a chargegenerating layer is composed of a polymer layer having a distyrylcompound dispersed therein (refer to Japanese Patent ApplicationLaid-Open No. 157660/1991). However, the above-mentioned devices havebeen complicated in production because of the necessity of adding a newlayer to the device.

In addition, there is disclosed an organic EL device technology whichenhances a positive-hole injecting efficiency into an organiclight-emitting layer by the use of a injecting layer comprising anaromatic tertiary amine (refer to Japanese Patent Application Laid-OpenNo. 295695/1988). Nevertheless the above-disclosed device does not fullysatisfy electric power conversion efficiency and light-emittingefficiency. Thus, there is required an EL device capable of being drivenby a lower voltage in order to enhance the power conversion efficiencyand light-emitting efficiency of the device.

There is also disclosed an organic EL device technology whichconstitutes a light-emitting layer by mixing a styrylamine derivativebeing a positive-hole transporting material and also a light emittingmaterial with an oxadiazole derivative being an electron transportingmaterial (refer to Japanese Patent Application Laid-Open No.250292/1990). However, the aforesaid technology relates to theincorporation of an oxadiazole derivative into a light emitting layercomprising a styrylamine to impart electron injecting properties to thelayer, and discloses nothing about such function of a charge injectionauxiliary material that improves charge injecting properties by adding aslight amount of a styrylamine to a light emitting layer (not being astyrylamine layer in most cases) or to an electron transporting layer.

There are known an EL device having an organic light-emitting layer inwhich 8-hydroxyquinoline aluminum complex as the host is doped with aslight amount of a fluorescent substance (refer to Japanese PatentApplication Laid-Open No. 264692/1988) and an organic light-emittinglayer in which 8-hydroxyquinoline aluminum complex as the host is dopedwith a quinacridone-based pigment (refer to Japanese Patent ApplicationLaid-Open No. 255190/1991). Nevertheless, the above-mentioned dopants donot function as a charge injection auxiliary material.

DISCLOSURE OF THE INVENTION

Under such circumstances, intensive research and investigations weremade by the present inventors in order to develop a charge injectionauxiliary material capable of enhancing charge injecting properties byadding a slight amount thereof in a functional layer such as alight-emitting layer in an organic electron device. As a result, it hasbeen found by the present inventors that a derivative of stilbene,distyrylarylene or tris(styrylarylene) each having an electron donatingproperty is useful as a charge injection auxiliary material and that anorganic electroluminescence device containing the aforesaid chargeinjection auxiliary material and having an energy gap in alight-emitting layer higher than that in said charge injection auxiliarymaterial is lowered in applied voltage, enhanced in luminous efficiencyand prolonged in service life. The present invention has beenaccomplished on the basis of the aforestated finding and information.

Specifically the present invention provides a charge injection auxiliarymaterial for use in an organic electron device wherein a functionallayer composed of a positive-hole transporting organic substance issubjected to positive-hole injection from an external layer byincorporating said material in said functional layer which materialcomprises a derivative of stilbene, distyrylarylene ortris(styrylarylene).

In addition, the present invention provides an organicelectroluminescence device which comprises the above-mentioned chargeinjection auxiliary material and the light emitting layer characterizedin that the ionization energy of the charge injection auxiliary materialis smaller than the ionization energy of the light emitting layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration showing the energy level in anorganic electron device.

FIG. 2 is a schematic illustration showing the energy level in anorganic electroluminescence device.

In FIG. 1, symbol 11 is a conduction level of the functional layer,symbol 12 is a valence level of the functional layer, symbol 13 is avalence level of the charge injection auxiliary material, and symbol 14is a work function of anode or a valence level of the external layer. InFIG. 2, symbol 21 is a conduction level of the light emitting layer,symbol 22 is a valence level of the light emitting layer, symbol 23 is avalence level of the charge injection auxiliary material, symbol 24 is awork function of the anode, and symbol 25 is a work function of cathode.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

The charge injection auxiliary material according to the presentinvention is employed for the purpose of enhancing the charge injectingproperties at the same electric field strength and injecting a largeramount of charge in the case where positive holes are injected from anexternal layer into a charge-transporting functional layer. The amountof the charge injection auxiliary material to be added in the functionallayer comprising an organic substance is preferably 19% or less byweight, particularly preferably 0.05 to 9% by weight based on the weightof the functional layer.

Accordingly, a charge injection auxiliary material is distinguished froma charge transporting material, namely a charge transporting material ina photosensitive body, a light emitting material in an organic ELdevice, a semiconductor in an organic transistor, and is a material usedfor the purpose of enhancing charge injecting properties by being addingin the above-mentioned functional layer comprising a charge transportingmaterial as the principal component thereof.

In addition, the term "functional layer" signifies a layer whichpreserves the function of transporting or injecting positive holes andis exemplified by a positive-hole injecting layer, a positive-holetransporting layer, a light emitting layer and an electron barrierlayer.

In the following, the function of the charge injection auxiliarymaterial will be described with reference to FIG. 1.

FIG. 1 is a schematic illustration showing the energy level in anorganic electron device. In the case where positive holes are injectedfrom the energy level 14 to the energy level 12, the energy levelbarrier due to the difference between the energy levels 12 and 14 mustbe surmounted. When the charge injection auxiliary material having anenergy level 13 is added in the functional layer, positive holes aremore easily injected at the energy level 13, and the movement ofpositive holes to the level 12 takes precedence over the movementthereof within the level 13, since a slight amount of the chargeinjection auxiliary material is already dispersed in the functionallayer. Thereby the charge injecting properties are enhanced. The chargeinjection auxiliary material according to the present invention isexcellent in charge injection auxiliary function.

The stilbene derivative to be used as the charge injection auxiliarymaterial according to the present invention is a compound in which atleast two aromatic rings are bonded by way of a vinyl group or asubstituted vinyl group, and any of the aforementioned aromatic ringsand vinyl group bears an electron donating group.

The distyrylarylene derivative is a compound in which two aromatic ringsare bonded to one arylene group each by way of a vinyl group or asubstituted vinyl group, and an electron donating group is contained.

In addition, the tris(styrylarylene) derivative is a compound in whichthree aromatic rings are bonded to one trivalent aromatic ring radicalby way of a vinyl group or a substituted vinyl group, and an electrondonating group is contained.

In the above-mentioned derivative containing an electron donating groupin its molecular skeleton, the electron donating group is exemplifiedpreferably by an alkoxy group having 1 to 10 carbon atoms, an aryloxygroup having 6 to 10 carbon atoms and an amino group with a hydrocarbonradical having 1 to 30 carbon atoms.

The particularly preferable derivatives in the present invention are thecompounds represented by any of the following general formulae (I) to(VII), wherein (I) and (II) stand for a stilbene derivative, (III) and(IV) denote a distyrylarylene derivative, and (V) to (VII) indicate atris(styrylarylene) derivative. ##STR1## wherein Ar¹ is an aryl grouphaving 6 to 20 carbon atoms, a thienyl group or a bithienyl group, R¹ toR⁴ are each a hydrogen atom, an aryl group having 6 to 20 carbon atoms,a thienyl group or a bithienyl group, R¹ and R², and R³ and R⁴ may eachbe same or different, respectively, D¹ to D³ are each an aryl grouphaving 6 to 20 carbon atoms which is substituted with an electrondonating group, a thienyl group or a bithienyl group or a condensedpolycyclic group having 10 to 30 carbon atoms, D² and D³ may be same ordifferent, and Ar¹ and R¹ to R⁴ may each be unsubstituted or substitutedwith an alkyl group having 1 to 10 carbon atoms, an alkoxy group having1 to 10 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, anarylalkyl group having 7 to 10 carbon atoms or an amino group with ahydrocarbon radical having 1 to 20 carbon atoms. ##STR2## wherein Ar²and Ar³ are each an arylene group having 6 to 20 carbon atoms, athienylene group or a bithienylene group, Ar₄ is an aryl group having 6to 20 carbon atoms, a thienyl group or a bithienyl group, R⁵ to R¹² areeach a hydrogen atom, an aryl group having 6 to 20 carbon atoms, athienyl group or a bithienyl group, R⁵ to R⁸ ; and R⁹ to R¹² may each besame or different, respectively, D⁴ to D⁶ are each an aryl group having6 to 20 carbon atoms which is substituted with an electron donatinggroup, a thienyl group or a bithienyl group or a condensed polycyclicgroup having 10 to 30 carbon atoms, D⁴ and D⁵ may be same or different,and Ar² to Ar⁴ and R⁵ to R¹² may each be unsubstituted or substitutedwith an alkyl group having 1 to 10 carbon atoms, an alkoxy group having1 to 10 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, anarylalkyl group having 7 to 10 carbon atoms or an amino group with ahydrocarbon radical having 1 to 20 carbon atoms. ##STR3## wherein Ar⁵ toAr⁷ are each a trivalent aromatic ring radical having 6 to 24 carbonatoms, Ar⁸ to Ar¹⁰ are each an aryl group having 6 to 20 carbon atoms, athienyl group or a bithienyl group, Ar⁹ and Ar¹⁰ may be same ordifferent, R¹³ to R³⁰ are each a hydrogen atom, an aryl group having 6to 20 carbon atoms, a thienyl group or a bithienyl group, R¹³ to R¹⁸ ;R¹⁹ to R²⁴ ; and R²⁵ to R³⁰ may be each same or different, respectively,D⁷ to D¹² are each an aryl group having 6 to 20 carbon atoms which issubstituted with an electron donating group, a thienyl group or abithienyl group or a condensed polycylic group having 10 to 30 carbonatoms, D⁷ to D⁹, D¹⁰ and D¹¹ may be same or different, and Ar⁵ to Ar¹⁰and R¹³ to R³⁰ may be each unsubstituted or substituted with an alkylgroup having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbonatoms, an aryloxy group having 6 to 10 carbon atoms, an arylalkyl grouphaving 7 to 10 carbon atoms or an amino group with a hydrocarbon radicalhaving 1 to 20 carbon atoms.

The aryl group having 6 to 20 carbon atoms in the above-mentionedgeneral formulae (I) to (VII) is exemplified preferably by a phenylgroup, biphenylyl group, naphthyl group, pyrenyl group, terphenylylgroup, anthranyl group, tolyl group, xylyl group and monovalent groupcomprising stilbene.

The arylene group having 6 to 20 carbon atoms therein is exemplifiedpreferably by a phenylene group, biphenylene group, naphthylene group,anthranylene group, terphenylene group, pyrenylene group and divalentgroup comprising stilbene.

The trivalent aromatic ring radical having 6 to 24 carbon atoms isexemplified preferably by the following groups: ##STR4##

Examples of the aryloxy group having 6 to 20 carbon atoms as theabove-mentioned substituent include a phenyloxy group, and biphenyloxygroup, naphthyloxy group, anthranyloxy group, terphenyloxy group andpyrenyloxy group; examples of the alkyl group having 1 to 10 carbonatoms include a methyl group, ethyl group, isopropyl group, tert-butylgroup, pentyl group and hexyl group; examples of the alkoxy group having1 to 10 carbon atoms include a methoxy group, ethoxy group, isopropoxygroup, tert-butoxy group and pentyloxy group; and examples of the aminogroup with a hydrocarbon radical having 1 to 20 carbon atoms include adimethylamino group, diethylamino group, diphenylamino group,phenylethylamino group, phenylmethylamino group, ditolylamino group,ethylphenylamino group, phenylnaphthyl amino group andphenylbiphenylamino group.

The D¹ to D² in the above-mentioned general formulae (I) to (VII) areeach an aryl group having 6 to 20 carbon atoms which is substituted withan electron donating group, a thienyl group or a bithienyl group or acondensed polyoylic group having 10 to 30 carbon atoms. The electrondonating group as mentioned herein is exemplified preferably by analkoxy group having 1 to 10 carbon atoms, an aryloxy group having 6 to20 carbon atoms, particularly preferably by an amino group with ahydrocarbon radical having 1 to 30 carbon atoms. The aforesaid aminogroup can be exemplified by the group represented by the general formula##STR5## wherein X¹ to X² are each an alkyl group having 1 to 10 carbonatoms, an aryl group having 6 to 20 carbon atoms, a thienyl group, abithienyl group or an arylalkyl group having 7 to 20 carbon atoms andmay be same or different and be bonded to each other to form a saturatedor unsaturated cyclic structure, and they may be a substituted alkylgroup having 1 to 10 carbon atoms, a substituted alkoxy group having 1to 10 carbon atoms, a substituted aryloxy group having 6 to 10 carbonatoms or a substituted arylalkyl group having 7 to 10 carbon atoms.

Preferable examples of the above-mentioned electron donating groupinclude an alkoxy group or aryloxy group such as phenyoxy group,biphenyloxy group, naphthyloxy group, anthranyloxy group, terphenylyloxygroup, methoxy group, ethoxy group, isopropoxy group, tert-butyloxygroup and pentyloxy group, and an amino group having a hydrocarbonradical such as dimethylamino group, diethylamino group, diphenylaminogroup, phenylmethylamino group, phenylethylamino group,phenylmethylethylamino group, ditolylamino group, ethylphenylaminogroup, phenylnaphthylamino group and phenylbiphenylylamino group.Specific examples of the D¹ to D¹² include the following: ##STR6##

Specific examples of the compound represented by any of the generalformulae (I) to (VII) include the following: ##STR7##

Particularly preferable compound among the charge injection auxiliarymaterials represented by any of the general formulae (I) to (VII) is thedistyrylarylene derivative represented by any of the general formulae(III) and (IV), which has a remarkable charge injection assistantfunction.

In the following, the principle of the charge injection auxiliarymaterial when applied to an organic EL device will be described withreference to FIG. 2, which is an energy level drawing prepared fordescribing the principle of the charge injection auxiliary material inthe organic EL device comprising an anode/a light emitting layer/acathode.

Positive holes among the charges are injected,under applied electricfield at the valence electron level 23 of the charge injection auxiliarymaterial, since it is easier than the injection at the valence level ofthe light emitting layer. Then, the positive holes try to move towardsthe cathode at the valence level of the charge injection auxiliarymaterial, but are injected at the valence level of the light emittinglayer because of a large intermolecular distance in the charge injectionauxiliary material. The positive holes, when arrive at the valence levelof the light emitting layer, move at the valence level and recombinewith the electrons moving at the conduction level injected from thecathode.

It is understood from the description that the charge injectionauxiliary material according to the present invention makes it easy toinject the positive holes in the light emitting layer usually atan,energy lower than the ionization energy of the light emitting layer.

Some of the charge injection auxiliary material has an energy gapsmaller than that of the light emitting layer. In such a case, theexcited state formed by the charge which has rejoined in the lightemitting layer is transferred to the charge injection auxiliary layer.

Since the charge injection auxiliary material which has been dispersedin a slight amount according to the present invention has a highfluorescence yield, the quantum yield of the EL device using the chargeinjection auxiliary material according to the present invention issometimes doubled or more.

As mentioned hereinbefore, the charge injection auxiliary material notonly enables a decrease in applied voltage and improvement in quantumyield but also exhibits a surprisingly remarkable effect on thestabilization of voltage as well as the brightness of the EL device.

The point to which special attention should be paid is that the chargeinjection auxiliary material is added preferably in a slight amount inorder to facilitate the movement at the valence level.

With regard to the organic EL device utilizing the above-mentionedcharge injection auxiliary material, the following structures arepossible in addition to the aforesaid structure.

(1) Anode/positive-hole injecting layer/light emitting layer/cathode

(2) Anode/positive-hole injecting layer/light emitting layer/electroninjecting layer/cathode

(3) Anode/light emitting layer/electron injecting layer/cathode

(4) Anode/organic semiconductor layer/light emitting layer/cathode

(5) Anode/organic semiconductor layer/electron barrier layer/lightemitting layer/cathode

(6) Anode/positive-hole injecting layer/light emitting layer/adhesionimproving layer/cathode

The objective device can be obtained by adding the charge injectionauxiliary material according to the present invention in theabove-mentioned light emitting layer, positive-hole injecting layer ororganic semiconductor layer.

In the aforestated device structure, the charge injection auxiliarymaterial has a molecular structure similar to that in the light emittinglayer (the host substance in the light emitting layer), as the case maybe, but the similar molecular structure does not cause any problem. Itis preferable that the host material occupies 81% or more by weight ofthe light emitting material, and the charge injection auxiliary materialoccupies 19% or less by weight of the light emitting material,particularly preferably in the range of 0.5 to 5% by weight basedthereon. In addition, it is particularly preferable that the ionizationenergy of the charge injection auxiliary material be lower than that ofthe light emitting material.

Moreover, it is particularly preferable that the difference in theionization energy between the light emitting material and the chargeinjection auxiliary material be not less than 0.1 eV.

The charge injection auxiliary material according to the presentinvention functions as a fluorescent dopant in addition to the chargeinjection assistant effect. By the term fluorescent dopant is meant asubstance which emits light in response to the recombining of positiveholes and electrons in the region consisting of the host material.

The present invention also provides an organic EL device which comprisesthe above-mentioned charge injection auxiliary material and the lightemitting material having an energy gap more than the energy gap of saidcharge injection auxiliary material. It is preferable in said organic ELdevice that the energy gap of the charge injection auxiliary material beless than the energy gap of the light emitting layer by 0.1 eV or more.The suitable organic EL device is such that emits light by being excitedthrough the recombination of positive holes and electrons in the lightemitting layer. Such organic EL device according to the presentinvention is characterized by lowered applied voltage, enhanced luminousefficiency and prolonged service life.

The charge injection auxiliary material according to the presentinvention is added in the functional layer of the organic electrondevice. In the case where the organic electron device is an organic ELdevice, said functional layer is a positive-hole injecting layer or alight emitting layer in the above-mentioned structures (1), (2) and (6);a light emitting layer in the structure (3); an organic semiconductorlayer or a light emitting layer in the structure (4); and an organicsemiconductor layer, an electron barrier layer or a light emitting layerin the structure (5).

The light emitting layer in the aforestated organic EL device, as is thecase with an ordinary light emitting layer, possesses an injectingfunction (it is capable of injecting positive holes from an anode orpositive hole injecting layer and besides injecting electron from acathode or electron injecting layer at the time of voltage beingapplied); a transporting function (it is capable of moving positive holeand electrons by an electric field force); and a light emitting function(it is capable of providing the rejoining field of positive holes andelectrons, thereby emitting light). The thickness of the functionallayer can be determined suitably according to the conditions withoutspecific limitation, and is preferably 1 nm to 10 μm, particularlypreferably 5 nm to 5 μm.

As the preferable light emitting material (host material), mention canbe made of the compound represented by the general formula (IX) ##STR8##wherein Y¹ to Y⁴ indicate each a hydrogen atom, an alkyl group having 1to 6 carbon atoms, an alkoxyl group having 1 to 6 carbon atoms, anaralkyl group having 7 to 8 carbon atoms, a substituted or unsubstitutedaryl group having 6 to 18 carbon atoms, a substituted or unsubstitutedcyclohexyl group, a substituted or unsubstituted aryloxyl group having 6to 18 carbon atoms, or an alkoxyl group having 1 to 6 carbon atoms;therein, the substituent is an alkyl group having 1 to 6 carbon atoms,an alkoxyl group having 1 to 6 carbon atoms, an aralkyl group having 7to 8 carbon atoms, an aryloxy group having 6 to 18 carbon atoms, an acylgroup having 1 to 6 carbon atoms, an acyloxy group having 1 to 6 carbonatoms, a carboxyl group, a styryl group, an arylcarbonyl group having 6to 20 carbon atoms, an aryloxycarbonyl group having 6 to 20 carbonatoms, an alkoxycarbonyl group having 1 to 6 carbon atoms, a vinylgroup, an anilinocarbonyl group, a carbamoyl group, a phenyl group, anitro group, a hydroxyl group or a halogen; these substituents may beused solely or in plural; Y¹ to Y⁴ may be identical to or different fromone another, and Y¹ and Y² and Y.sup. 3 and Y⁴ may combine with groupssubstituting each other to form a substituted or unsubstituted saturatedfive-membered ring or a substituted or unsubstituted saturatedsix-membered ring; Ar indicates a substituted or unsubstituted arylenegroup having 6 to 20 carbon atoms, which may be mono-substituted orpoly-substituted, and in which its bonding position may be any ofortho-, para- and meta-; however, when Ar is an unsubstituted phenylene,Y¹ to Y⁴ is each selected from the group consisting of an alkoxyl grouphaving 1 to 6 carbon atoms, an aralkyl group having 7 to 8 carbon atoms,a substituted or unsubstituted naphthyl group, a biphenyl group, acyclohexyl group, and an aryloxy group, general formula (X):

    A--Q--B                                                    (X)

wherein A and B indicate each a monovalent group which is obtained byremoving a hydrogen atom from the compound represented by the abovegeneral formula (IX), and may be identical to or different from eachother; Q indicates a divalent group breaking the conjugation, or generalformula (XI) ##STR9## wherein A¹ indicates a substituted orunsubstituted arylene group having 6 to 20 carbon atoms or a divalentaromatic heterocyclic group; its bonding position may be any of ortho-,meta- and para-; A² is a substituted or unsubstituted aryl group having6 to 20 carbon atoms or a monovalent aromatic heterocyclic group; Y⁵ andY⁶ indicate each a hydrogen atom, a substituted or unsubstituted arylgroup having 6 to 20 carbon atoms, a cyclohexyl group, a monovalentaromatic heterocyclic group, an alkyl group having 1 to 10 carbon atoms,an aralkyl group having 7 to 20 carbon atoms or an alkoxyl group having1 to 10 carbon atoms; Y⁵ and Y⁶ may be identical to or different fromeach other; the mono-substituent therein is an alkyl group, an aryloxygroup, an amino group or a phenyl group with or without a substituent;each substituent of Y⁵ may combine with A¹ to form a saturated orunsaturated five-membered ring or six-membered ring, and similarly eachsubstituent of Y⁶ may combine with A² to form a saturated or unsaturatedfive-membered ring or six-membered ring; Q indicates a divalent groupbreaking a conjugation,

The symbol Q in the general formulae (X) and (XI) indicates a divalentgroup breaking a conjugation. The conjugation therein is attributable tothe delocalization of π-electron, and includes a conjugated double bondor a conjugation due to an unpaired electron or a lone electron-pair.Specific examples of Q include ##STR10##

The divalent group breaking the conjugation is thus used in order thatEL emission light Obtained when the compound forming A or B shown inabove (that is, the compound of general formula (IX)) is used solely asthe organic EL device of the present invention and the EL emission lightobtained when the compound represented by general formula (X) is used asthe organic EL device of the present invention may be identical incolor. In other words, said divalent group is used so that thewavelength of the light emitting layer using the compound represented bygeneral formula (IX) or general formula (X) may not be changed toshortened or lengthened. By combining with a divalent group to breakconjugation, it is confirmed that the glass transition temperature (Tg)rises, and uniform pinhole free minute crystal or amorphous thin filmcan be obtained, improving the uniformity of light emission. Further,combining with a divalent group breaking the conjugation brings aboutadvantages that EL emission is not long-wavened, and synthesis orpurification can easily be effected.

As another preferable light emitting material (host material), mentioncan be made of a metal complex of 8-hydroxyquinoline or derivativethereof. Specific examples of them include metal chelated oxinoidecompound containing a chelate of oxine (generally, 8-quinolinol or8-hydroxyquinoline). Such compound exhibits a high level performance,and is easy to be formed into a thin film. Examples of the oxinoidecompounds satisfy the following structural formula. ##STR11## wherein Mtindicates a metal, n is an integer of 1 to 3, and Z indicates an atomrequired to complete at least two condensed aromatic ring, being locatedindependently.

Therein the metal represented by Mt is a monovalent, divalent ortrivalent metal, that is, an alkali metal such as lithium, sodium orpotassium, an alkaline earth metal such as magnesium or calcium, or anearth metal such as boron or aluminum.

Generally any of monovalent, divalent and trivalent metals which areknown to be useful chelated compounds can be used therein.

Z indicates an atom to form a hetero ring comprising azole or azine asone of at least two condensed aromatic rings. Herein, if necessary,another ring can be added to the above-mentioned condensed aromaticring. Moreover, in order to avoid adding bulky molecules withoutimprovement in function, the number of the atoms shown by Z ispreferably kept to not more than 18.

Further, specific examples of the chelated oxinoide compounds includetris(8-quinolinol)aluminum, bis(8-quinolinol) magnesium,bis(benzo-8-quinolinol)zinc, bis(2-methyl-8-quinolato)aluminum oxide,tris(8-quinolinol)indium, tris(5-methyl-8-quinolinol)aluminum,8-quinolinol lithium, tris(5-chloro-8-quinolinol)gallium,bis(5-chloro-8-quinolinol)calcium,tris(5,7-dichloro-8-quinolinol)aluminum andtris(5,7-dibromo-8-hydroxyquinolinol)aluminum.

The above-mentioned light emitting layer can be prepared by forming theabove compound into a thin film by a known method such as the vapordeposition method, the spin-coating method, the casting method or the LBmethod, and particularly, a molecular accumulated film is preferable. Amolecular accumulated film therein is a thin film formed by depositingsaid compound from a gaseous state, or a thin film formed bysolidification of said compound from a molten state. Usually, saidmolecular accumulated film is distinguished from a thin film (molecularbuilt-up film) formed by the LB method by the difference in theaggregation structure or the higher-order structure, or the functionaldifference resulting therefrom.

The above-mentioned light emitting layer can be formed by dissolving abinding agent such as a resin and said compound in a solvent to preparesolution, which is formed into a thin film by the spin-coating method orthe like.

The film thickness of the light emitting layer thus formed is notparticularly limited, but can be determined appropriately according tothe circumstances. Usually, it is preferably in the range of 1 nm to 10μm, particularly preferably 5 nm to 5 μm.

Herein examples of compounds represented by any of the aforesaid generalformulae (IX) to (XI) to be used as the above-mentioned light emittinglayer are shown as follows. ##STR12##

As to the anode in the organic EL device of the present invention, ametal, an alloy, an electroconducting compound or a mixture thereof, allhaving a large work function (not less than 4 eV), is preferably used asan electrode material. Specific examples of these electrode materialsare metals such as Au, and a dielectric transparent materials such asCul, ITO, SnO², and ZnO. The anode can be prepared by forming theelectrode material into a thin film by vapor deposition or sputtering.To obtain light emission from the electrode, it is preferable that thetransmittance of the electrode be more than 10% and the resistance ofthe sheet as an electrode be not more than several hundred Ω/□. The filmthickness of the anode is usually in the range of 10 nm to 1 μm,preferably 10 to 20 nm, depending upon the material.

On the other hand, as the cathode, a metal, an alloy, anelectroconducting compound or a mixture thereof, all having a small workfunction (not more than 4 eV) is preferably used as an electrodematerial. Specific examples of such electrode materials are sodium, asodium-potassium alloy, magnesium, lithium, a magnesium-silver alloy,Al/AlO₂, indium, and rare earth metals. The cathode can be prepared byforming the electrode material into a thin film by vapor deposition orsputtering. The resistance of the sheet as an electrode is preferablynot more than several hundred Ω/□. The film thickness is usually in therange of 10 nm to 1 μm, preferably 50 to 200 nm. In the EL device of thepresent invention, it is preferable that either anode or cathode betransparent or translucent because light emission is transmitted andobtained with a high efficiency by such property.

Next, the hole injecting layer in the present invention is notnecessarily required for the present device, but is preferably used forthe purpose of improving the emission performance. The preferablematerial of said hole-injecting layer is one which transports holes tothe light emitting layer at a lower electric field, and still morepreferably the mobility of holes is made at least 10⁻⁶ cm² /volt.sec inat an applied electric field of 10⁴ to 10⁶ volt/cm. In order to maintainelectrons in the light emitting layer, an electron barrier layer may beused between the light emitting layer and the anode.

As the positive hole injecting material, an arbitrary material can beselected and used from the conventionally used ones as the electriccharges transporting material for holes and the known ones to be usedfor the hole-injecting layer of EL devices in conventionalphoto-conducting materials without specific limitation, provided thatthe material has the aforesaid favorable properties.

Examples of the materials a for hole-injecting layer include triazolederivatives (described in the specification of U.S. Pat. No. 3,112,197,etc.), oxadiazole derivatives (described in the specification of U.S.Pat. No. 3,189,447, etc.), imidazole derivatives (described in JapanesePatent Publication No. 16096/1962, etc.), polyarylalkane derivatives(described in the specifications of U.S. Pat. Nos. 3,615,402, 3,820,989and 3,542,544, and in Japanese Patent Publication Nos. 555/1970 and10983/1976, and further in Japanese Patent Application Laid-Open Nos.93224/1976, 17105/1980, 4148/1981, 108667/1980, 156953/1980 and36656/1981, etc.), pyrazoline derivatives or pyrazolone derivatives(described in the specifications of U.S. Pat. Nos. 3,180,729 and4,278,746, and in Japanese Patent Application Laid-Open Nos. 88064/1980,88065/1980, 105537/1974, 51086/1980, 80051/1981, 88141/1981, 45545/1982,112637/1979 and 74546/1970, etc.), phenylenediamine derivatives(described in the specification of U.S. Pat. No. 3,615,404, and inJapanese Patent Publication Nos. 10105/1976, 3712/1971 and 25336/1972,and further in Japanese Patent Application Laid-Open Nos. 53435/1979,110536/1979 and 119925/1979, etc.), arylamine derivatives (described inthe specification of U.S. Pat. Nos. 3,567,450, 3,180,703, 3,240,597,3,658,520, 4,232,103, 4,175,961 and 4,012,376, and in Japanese PatentPublication Nos. 35702/1974 and 27577/1964, and further in JapanesePatent Application Laid-Open Nos. 144250/1980, 119132/1981 and22437/1981, and German Patent No. 1,110,518, etc.), amino-substitutedchalcone derivatives (described in the specification of U.S. Pat. No.3,526,501, etc.), oxazole derivatives (described in the specification ofU.S. Pat. No. 3,257,203, etc.), styrylanthracene derivatives (describedin Japanese Patent Application Laid-Open No. 46234/1981, etc.),fluorenone derivatives (described in Japanese Patent ApplicationLaid-Open No. 110837/1979, etc.), hydrazone derivatives (described inthe specification of U.S. Pat. No. 3,717,462, and in Japanese PatentApplication Laid-Open Nos. 59143/1979, 52063/1980, 52064/1980,46760/1980, 85495/1980, 11350/1982 and 148749/1982, etc.), and stilbenederivatives (described in Japanese Patent Application Laid-Open Nos.210363/1986, 228451/1986, 14642/1986, 72255/1986, 47646/1987,36674/1987, 10652/1987, 30255/1987, 93445/1985, 94462/1985, 174749/1985,and 175052/1985, etc.)

Further, other examples thereof include silazane derivatives (describedin the specification of U.S. Pat. No. 4,950,950), polysilane basedmaterial (described in Japanese Patent Application Laid-Open No.204996/1990), aniline-based copolymer (described in Japanese PatentApplication Laid-Open No. 282263/1990), and electrically conductive highmolecular oligomer disclosed in the specification of Japanese PatentApplication Laid-Open No. 211399/1989, among them, thiophene oligomer.

In the present invention, the above compounds can be used as ahole-injecting material, but it is preferred to use porphyrin compounds(described in Japanese Patent Application Laid-Open No. 2956965/1988,etc.), aromatic tertiary amine compounds or styrylamine compounds(described in the specification of U.S. Pat. No. 4,127,412, and JapanesePatent Application Laid-Open Nos. 27033/1978, 58445/1979, 149634/1979,64299/1979, 79450/1980, 144250/1980, 119132/1981, 295558/1986,98353/1986 and 295695/1988), and most preferably, said aromatic tertiaryamine compounds are used.

Typical examples of the aforesaid porphyrin compounds are porphin;1,10,15,20-tetraphenyl-21H,23H-porphin copper (II);1,10,15,20-tetraphenyl-21H,23H-porphin zinc (II);5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphin;siliconphthalocyanine oxide, aluminum phthalocyanine chloride;phthalocyanine (nonmetal); dilithium phthalocyanine; coppertetramethylphthalocyanine; copper phthalocyanine; chrome phthalocyanine;zinc phthalocyanine; lead phthalooyanine; titanium phthalocyanine oxide;magnesium phthalocyanine; and copper octamethylphthalooyanine.

Typical examples of the aforesaid aromatic tertiary amine compounds orstyrylamine compounds are N,N,N',N'-tetraphenyl-4,4'-diaminophenyl;N,N'-diphenyl-N,N'-di(3-methylphenyl)-4,4'-diaminobiphenyl;2,2-bis(4-di-p-tolylaminophenyl)propane;1,1-bis(4-di-p-tolylaminophenyl)cyclohexane;N,N,N',N'-tetra-p-tolyl-4,4'-diaminobiphenyl;1,1-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane;bis(4-dimethylamino-2-methylphenyl) phenylmethane;bis(4-di-p-tolylaminophenyl)phenylmethane;N,N'-diphenyl-N,N'-di(4-methoxyphenyl)-4,4'-diaminobiphenyl;N,N,N',N'-tetraphenyl-4,4'-diaminodiphenyl ether;4,4'-bis(diphenylamino)quadriphenyl; N,N,N-tri(p-tolyl)amine;4-(di-p-tolylamino)-4'-[4(di-p-tolylamino)styryl]stilbene;4-N,N-diphenylamino-(2-diphenylvinyl)benzene;3-methoxy-4'-N,N-diphenylaminostilbene; N-phenylcarbazole; and aromaticdimethylidine-based compounds.

The hole injecting layer in the EL device of the present invention canbe obtained by forming the above compound into a film by the knownmethod of film forming such as the vacuum deposition method, the spincoating method, or the LB method. The film thickness as said holeinjecting layer is not particularly limited, but usually 5 nm to 5 μm.

The hole injecting layer may consist of one layer comprising one or twoor more of these hole-injecting materials, or may be a laminate of theaforesaid hole injecting layer and a hole injecting layer comprisingother compound than the before-mentioned hole injecting layer.

As materials for the organic semiconductor layer, mention can be made ofthe following compounds. ##STR13##

As materials for the electron barrier layer, mention may be made of thefollowing compounds. ##STR14##

In addition, there may be used, between the light emitting layer and thecathode, an adhesive layer having excellent transmitting property forelectrons and favorable adhesivity to the cathode (i.e., an electroninjecting layer, adhesion improving layer).

An adhesive layer to be freshly added preferably contains a materialhaving high adhesivity to both the light emitting layer and the cathode.Such material with high adhesivity thereto is exemplified by a metalcomplex of 8-hydroxyquinoline or derivative thereof, specifically ametal chelated oxinoide compound containing a chelate of oxine(generally, 8-quinolinol or 8-hydroxyquinoline).

Moreover, there may be employed a layer comprising an oxadiazolederivative in place of the adhesive layer.

As the oxadiazol derivative, mention is made of an electron transmittingcompound represented by any of the general formulae (XII) and (XIII)##STR15## wherein Ar¹¹ to Ar¹⁴ are each a substituted or unsubstitutedaryl group, Ar¹¹ and Ar¹², and Ar¹³ and Ar¹⁴ may be each identical to ordifferent from one another, and A¹⁵ is a substituted or unsubstitutedarylene group. Examples of the aryl group include a phenyl group,biphenyl group, anthracenyl group, perylenyl group and pyrenyl group.Examples of arylene group include a phenylene group, naphthylene group,biphenylene group, anthracenylene group, perylenylene group andpyrenylene group. Examples of the substituent include an alkyl grouphaving 1 to 10 carbon atoms, an alkoxyl group having 1 to 10 carbonatoms and a cyano group. The electron transmitting compound ispreferably a thin-film forming compound.

Specific examples of the above-mentioned electron transmitting compoundinclude the following compound. ##STR16##

In the following, the present invention will be described in more detailwith reference to synthesis examples and working examples, which howevershall not be construed to limit the invention thereto.

Synthesis Example 1 (Synthesis of BCzVBi)

The phosphonic acid ester represented by the formula ##STR17## in anamount of 1.8 g was dissolved in 20 ml of DMSO in an atmosphere of argonand 1.0 g of potassium-tert-butoxide (tBuOK) was added to the resultantsolution. Thereafter 2.0 g of N-ethylearbazole-3-carboxyaldehyde wasadded to the mixture with stirring at room temperature for 5 hours.

To the resultant reaction mixture was added 100 ml of methanol, with theresult that yellow powder precipitated. A solution of I₂ in benzene wasadded to the powder to recrystallize the same with the result that 0.8 gof yellow powder was obtained. The resultant product had a melting pointof not lower than 300° C.

The determination results by proton nuclear magnetic resonance (¹H-NMR), infrared absorption (IR) spectrum and elemental analysis aregiven below.

(1) ¹ H-NMR [solvent; CDCl³, standard; tetramethylsilane (TMS)]

δ (ppm)=6.9 to 8.5 (m, 26H: central biphenylene ring/carb azole ring-H)

δ (ppm)=4.3 (q, 4H: ethyl-methylene (--CH₂ --))

δ (ppm)=1.4 (t, 6H: ethyl-methyl (--CH³))

(2) IR spectrum (KBr pellet method)

ν_(c)═c ; 1600 cm⁻¹ (C═C stretching vibration)

δ_(c--H) ; 975 cm⁻¹ (C--H out-of-plane deformation vibration)

(3) Elemental analysis (The values in parentheses are theoreticalvalues)

C: 88.82% (89.15%)

H: 5.98% (6.12%)

N: 4.45% (4.73%)

Molecular formula: C₄₄ H₃₆ N₂

It was confirmed from the above-mentioned determination result that theresultant compound was that represented by the formula ##STR18##

Synthesis Examples 2 to 8

Each compound was synthesized in the same manner as in Synthesis Example1 except that any of the aldehydes, solvent, base and any of thephosphonio acid esters as shown in Table 1 were used.

                                      TABLE 1                                     __________________________________________________________________________        Species                                                                   Syn-                                                                              of                                                                        thesis                                                                            chemical                                                                  Ex- com-                   Sol-                                               ample                                                                             pound                                                                              Aldehyde          vent                                                                              Base                                                                              Phosphonic acid ester                      __________________________________________________________________________    2   DPAVBi                                                                              ##STR19##        DMSO                                                                              tBuOK                                                                              ##STR20##                                 3   BCzVB                                                                               ##STR21##        DMSO                                                                              tBuOK                                                                              ##STR22##                                 4   DPAVBm                                                                              ##STR23##        DMSO                                                                              tBuOK                                                                              ##STR24##                                 5   BCzVBo                                                                              ##STR25##        DMSO                                                                              tBuOK                                                                              ##STR26##                                 6   DPAVBo                                                                              ##STR27##        DMSO                                                                              tBuOK                                                                              ##STR28##                                 7   DPAVB                                                                               ##STR29##        DMSO                                                                              tBuOK                                                                              ##STR30##                                 8   TCzVB                                                                               ##STR31##        DMSO                                                                              tBuOK                                                                              ##STR32##                                 __________________________________________________________________________

Synthesis Example 9

Synthesis of 1-(2-(4-methylphenyl)ethenyl)pyrene (MeSTPy)

8.05 g (20 mmol) of 4-methylbenzyltriphenylphosphonium chloride and 4.61g (20 mmol) of 1-pyrenecarboxyaldehyde were suspended in 150 ml ofethanol anhydride in an atmosphere of argon. Thereafter 40 ml (20 mmol)of 0.5 mole/liter solution of lithium ethoxide in ethanol was addeddropwise to the resultant suspension at room temperature over a periodof 30 minutes.

After the completion of the dropwise addition, stirring was carried outat room temperature for 30 minutes, and 20 ml of water was added to thesuspension to arrest the reaction. The reaction product thus obtainedwas filtered and the residual cake was washed with methanol. The washedcake was recrystallized from cyclohexane containing a slight amount ofiodine. As a result, yellow acicular crystal was obtained in an amountof 3.41 g (56% yield).

The resultant product had a melting point of 155° to 156° C.

The determination results by proton nuclear magnetic resonance (¹H-NMR), IR spectrum and elemental analysis are given below.

(1) ¹ H-NMR [solvent; CDCl₃, standard; tetramethylsilane (TMS)]

δ (ppm)=2.40 (s, 3H: benzyl-methyl H)

δ (ppm)=7.2 to 8.6 (m, 15H; aromatic/ethenyl H)

(2) Elemental analysis (The values in parentheses are theoreticalvalues)

C: 94.73% (94.70%)

H: 5.28% (5.30%)

Molecular formula: C₂₄ H₁₆

It was confirmed from the above-mentioned determination result that theresultant compound was MeSTPy.

Synthesis Example 10

Synthesis of 1-(2-(4-(4-phenylethenyl)phenyl)ethenyl)pyrene (STSTPy)

4.9 g (10 mmol) of 4-(2-phenylethenyl)benzyltriphenylphosphoniumchloride and 2.30 g (10 mmol) of 1-pyrenecarboxyaldehyde were suspendedin 100 ml of ethanol anhydride in an atmosphere of argon. Thereafter 40ml (20 mmol) of 0.5 mole/liter solution of lithium ethoxide in ethanolwas added dropwise to the resultant suspension at room temperature overa period of 30 minutes.

After the completion of the dropwise addition, stirring was carried outat room temperature for 30 minutes, and 10 ml of water was added to thesuspension to arrest the reaction. The reaction product thus obtainedwas filtered and the residual cake was washed with methanol. The washedcake was recrystallized from toluene containing a slight amount ofiodine. As a result, yellow acicular crystal was obtained in an amountof 2.11 g (52% yield).

The resultant product had a melting point of 259° to 260° C.

The determination results by proton nuclear magnetic resonance (¹H-NMR), IR spectrum and elemental analysis are given below.

(1) ¹ H-NMR [solvent; deuterated dimethyl sulfoxide (DMSO-d6). standard;tetramethylsilane (TMS), 100° C.]

δ (ppm)=7.2 to 8.4 (m, 22H; aromatic/ethenyl H)

(2) Elemental analysis (The values in parentheses are theoreticalvalues)

C: 94.54% to (94.55%)

H: 5.41% to (5.45%)

Molecular formula: C₃ H₂₂

It was confirmed from the above-mentioned determination result that theresultant compound was STSTPy.

Synthesis Example 11

Synthesis of 9-(2-phenylethenyl)anthracene (STA)

3.89 g (10 mmol) of benzyltriphenylphosphonium chloride and 2.06 g (10mmol) of 9-anthracenecarboxyaldehyde were suspended in 100 ml of ethanolanhydride in an atmosphere of argon. Thereafter 20 ml (10 mmol) of 0.5mole/liter solution of lithium ethoxide in ethanol was added dropwise tothe resultant suspension at room temperature over a period of 30minutes.

After the completion of the dropwise addition, stirring was carried outat room temperature for 30 minutes, and 10 ml of water was added to thesuspension to arrest the reaction. The reaction product thus obtainedwas filtered and the residual cake was washed with methanol. The washedcake was recrystallized from cyclohexane containing a slight amount ofiodine. As a result, yellow acicular crystal was obtained in an amountof 3.41 g (48% yield).

The resultant product had a melting point of 132° to 133° C.

The determination results by proton nuclear magnetic resonance (¹H-NMR), IR spectrum and elemental analysis are given below.

(1) ¹ H-NMR [solvent; CDCl₃, standard; tetramethylsilane (TMS)]

δ (ppm)=6.8 to 8.2 (m, 16H; aromatic/ethenyl H)

(2) Elemental analysis (The values in parentheses are theoreticalvalues)

C: 94.28% (94.25%)

H: 5.70% (5.75%)

Molecular formula: C₂₂ H₁₆

It was confirmed from the above-mentioned determination result that theresultant compound was STA.

Synthesis Example 12 (Synthesis of DPAVTP)

The phosphonic acid ester represented by the formula ##STR33## in anamount of 1.86 g and 2.5 g of 4-(N,N-diphenylamino) benzaldehyde weredissolved in 30 ml of DMSO in an atmosphere of argon and 0.9 g ofpotassium-tert-butoxide (t-BuOK) was added to the resultant solution toproceed with reaction at room temperature for 4 hours. The resultantproduct was allowed to stand overnight.

To the resultant reaction mixture was added 50 ml of methanol with theresult that yellow powder precipitated. After the purification of theprecipitate with silica gel column, the precipitate was recrystallizedfrom toluene with the result that 1.5 g of yellow powder was obtained.The resultant product had a melting point of 272.5° to 274.5° C.

The determination results by proton nuclear magnetic resonance (¹H-NMR), mass spectrometry and elemental analysis are given below.

(1) ¹ H-NMR [solvent; CDCl₃, standard; tetramethylsilane (TMB)]

δ (ppm)=6.9 to 7.6 (m, 44H; central terphenylene ring/vinyl

CH═CH/and triphenylamine ring-H)

(2) Mass spectrometry (FD-MS)

Only m/z=768 (z=1) and m/z=384 (z=2) were obtained against

C₅₈ H₄₄ N₂ =768

(3) Elemental analysis (The values in parentheses are theoreticalvalues)

C: 90.72% (90.59%)

H: 5.57% (5.77%)

N: 3.71% (3.64%)

It was confirmed from the above-mentioned determination result that theresultant compound was that represented by the formula ##STR34##

EXAMPLES 1 TO 8

Indium tin oxide (ITO) was provided on a 25 mm×75 mm×1.1 mm glasssubstrate (NA40, produced by HOYA Corporation) in a 100 nm thick film byvapor deposition method to obtain a transparent supporting substrate(produced by HOYA Corporation).

The substrate had been ultrasonically washed in isopropyl alcohol for 5minutes, dried by blowing nitrogen and, then subjected to UV ozonewashing for 10 minutes in an apparatus (UV 300; manufactured by SamcoInternational Institute Inc.). A substrate holder of a commerciallyavailable vapor deposition system (manufactured by ULVAC Co., Ltd.) wasfixed onto the transparent supporting substrate. Then 200 mg ofN,N'-bis(3-methylphenyl)-N,N'-diphenyl[1,1'-biphenyl]-4,4'-diamine(TPD)was placed in an electrically-heated boat made of molybdenum, 200 mg of4,4'-bis(2,2-diphenylvinyl)biphenyl (DPVBi) was placed in anotherelectrically heated boat made of molybdenum, further 200 mg of thecompound (A) (shown in Table 2) as the charge injection auxiliarymaterial was placed in another electrically heated boat made ofmolybdenum, and the vacuum chamber was depressurized to 1×10⁻⁴ Pa. Afterthat, the boat containing TPD was heated to 215° to 220° C., and TPD wasvapor-deposited on the transparent supporting substrate at a vapordeposition rate of 0.1 to 0.3 nm/sec to obtain a positive hole injectionlayer of 60 nm in film thickness. In this vapor deposition process, thesubstrate was at room temperature.

Without taking the substrate out of the vacuum chamber, DPVBi waslaminated in a thickness of 40 nm on the positive hole injection layerand simultaneously, the boat containing the compound (A) was heated tomix the compound (A) in the light emitting layer. As to the vapordeposition rate, the deposition rate of the compound (A) was set to thevalues in column (C) in Table 2 against the deposition rate of DPVBi incolumn (B) in Table 2. Therefore, the mixing Patio (ratio of thecompound (A) to the host material) was set to the values in column (D)in Table 2.

Subsequently, the pressure in the vacuum chamber was raised to theatmospheric pressure, an aluminum complex of 8-hydroxyquinoline as thematerial of the adhesive layer was newly placed in anelectrically-heated boat made of molybdenum, 1 g of magnesium ribbon wasplaced in an electrically heated boat made of molybdenum, and 500 mg ofsilver wire was placed in a tungsten basket. The pressure of vacuumchamber was reduced to 1×10⁻⁴ Pa. Then, the aluminum complex of8-hydroxyquinoline was vapor-deposited at a vapor deposition rate of0.01 to 0.03 nm/sec to form an adhesive layer with a film thickness of20 nm. In addition, silver and magnesium were simultaneouslyvapor-deposited at vapor deposition rate of 0.1 nm/sec and 1.4 nm/sec,respectively to form the cathode composed of the mixed electrode ofsilver and magnesium with a film thickness of 150 nm.

A voltage of 7 V was applied to the device thus obtained, andmeasurements were made of the current density and the brightness of thedevice to calculate the luminous efficiency of the same. The results aregiven in Table 2.

                  TABLE 2                                                         ______________________________________                                                                          (D)                                                                           Mixing ratio                                               (B)      (C)       (% by                                              (A)     (nm/sec) (nm/sec)  weight)                                     ______________________________________                                        Example 1                                                                              DPAVBi    2.8˜3.0                                                                          0.1˜0.13                                                                        3˜4                                 Example 2                                                                              BCzVB     3.5˜4.5                                                                          0.02    0.6˜0.4                             Example 3                                                                              BCzVBi    3.0˜4.0                                                                          0.7     15˜18                               Example 4                                                                              DPAVBm    2.7˜3.7                                                                          0.1˜0.13                                                                        3˜5                                 Example 5                                                                              BCzVBo    2.7˜3.7                                                                          0.1˜0.13                                                                        3˜5                                 Example 6                                                                              DPAVBo    3.0˜4.5                                                                          0.04    0.9˜1.3                             Example 7                                                                              DPAVB     3.0˜4.0                                                                          0.05    1.2˜1.6                             Example 8                                                                              TCzVB     2.5˜3.0                                                                          0.05˜0.07                                                                       1.6˜2.7                             Comparative                                                                            none      2        none    0                                         Example 1                                                                     ______________________________________                                               Current Bright-  Luminous                                                     density ness     efficiency                                                                              Luminous                                           (mA/cm.sup.2)                                                                         (cd/m.sup.2)                                                                           (lm/w)    color                                       ______________________________________                                        Example 1                                                                              15.0      230      0.7     bluish green                              Example 2                                                                              7.5       200      1.2     blue                                      Example 3                                                                              9.5       162      0.8     blue                                      Example 4                                                                              9.0       164      0.8     blue                                      Example 5                                                                              11.0      130      0.5     blue                                      Example 6                                                                              11.4      220      0.9     blue                                      Example 7                                                                              7.5       210      1.3     greenish                                                                      blue                                      Example 8                                                                              7.0       160      1.0     blue                                      Comparative                                                                            0.7        10      0.6     blue                                      Example 1                                                                     ______________________________________                                    

Remarks: The abbreviated compounds (A) are detailed as follows ##STR35##

As can be seen from Table 2, the examples having the compound (A) mixedtherein are increased in the amount of current flow in terms of currentdensity and is improved in charge injection properties, which leadswithout fail to a decrease in voltage required to be applied to thedevice.

Comparative Example 1

The procedure in Example 1 was repeated to prepare the device exceptthat the use of the compound (A) was omitted.

The device thus obtained had a single luminous peak wavelength of 472nm.

EXAMPLE 9

The procedure in Example 1 was repeated to prepare the device exceptthat DPAVBi as the compound (A) was incorporated in DPVBi in an amountof 3% by weight, the film thickness of the light emitting layer (mixedlayer of DPAVBi and DPVBi) was set at 55 nm, and the film thickness ofthe positive hole injecting layer was set at 45 nm.

A voltage of 8 V was applied to the device thus obtained, with theresults that there was obtained a light emission having a currentdensity of 7 mA/cm², brightness of 400 cd/m² and peak wavelength of 494nm. The resultant light emission constituted the spectrum having threepeaks at 462 nm, 494 nm and 534 nm, which demonstrates that DPAVBi emitslight. The luminous efficiency thereof was 2.2 lumen/W and wassurpassingly excellent as compared with that of the comparative example.It is also pointed out that the charge injection auxiliary materialexhibits fluorescent doping effect as the case may be.

EXAMPLE 10

The procedure in Example 1 was repeated to prepare the device exceptthat the aluminum complex of 8-hydroxyquinoline was used as the lightemitting material, STP was used as the charge injection auxiliarymaterial, the mixing ratio thereof was set at 0.7% by weight and thefilm thickness of the light emitting layer was set at 40 nm. A voltageof 5.5 V was applied to the device thus obtained, with the result thatthere was obtained a green light emission having a current density of 23mA/cm² and brightness of 1000 cd/m². The luminous efficiency thereof was2.4 lumen/W. ##STR36##

Comparative Example 2

The procedure in Example 1 was repeated to prepare the device exceptthat the aluminum complex of 8-hydroxyquinoline was used as the lightemitting material and the use of the compound (A) was omitted.

A voltage of 7 V was applied to the device thus obtained, with theresult that there was obtained a green light emission having a currentdensity of 23 mA/cm² and brightness of 780 cd/m². The luminousefficiency thereof was 1.5 lumen/W.

Comparative Example 3

The procedure in Example 1 was repeated to prepare the device exceptthat DPVBi was used as the host material,3-(2'-benzothiazolyl)-7-diethylamino-coumarin (KU 7: Japanese PatentApplication Laid-Open No. 264692/1988) was used in place of the chargeinjection auxiliary material, and the mixing ratio thereof was set at 2%by weight.

A voltage of 7 V was applied to the device thus obtained, with theresult that there was obtained a green light emission having a currentdensity of 5 mA/cm² and brightness of 150 Cd/m².

It is understood by the result of comparing Comparative Examples 2 and 3with Example 10 that the device comprising the charge injectionauxiliary material according to the present invention attains a decreasein voltage required to be applied to the device as well as anenhancement in luminous efficiency. In addition, the device containingcoumarin 7 (KU 7) as the dopant causes the applied charge to increase.

EXAMPLES 11 TO 13

The procedures in Examples 1 to 8 were repeated to prepare the devicesexcept that UV washing was carried out for 30 minutes. A voltage of 7 Vwas applied to the device thus obtained, and measurements were made ofthe current density and the brightness of the device to calculate theluminous efficiency of the same. The results obtained are given in Table3.

                  TABLE 3                                                         ______________________________________                                                                         (D)                                                        (B)      (C)       Mixing ratio                                        (A)    (nm/sec) (nm/sec)  (% by weight)                                ______________________________________                                        Example 11                                                                             STSTPy   2.5˜3.2                                                                          0.1˜0.12                                                                        3.2 approx.                                Example 12                                                                             MeSTPy   2.7˜3.7                                                                          0.1˜0.12                                                                        3.2 approx.                                Example 13                                                                             STPy     3.0˜3.5                                                                          0.06      2 approx.                                ______________________________________                                               Current Bright-  Luminous                                                     density ness     efficiency                                                                              Luminous                                           (mA/cm.sup.2)                                                                         (cd/m.sup.2)                                                                           (lm/W)    color                                       ______________________________________                                        Example 11                                                                             7.0       101      0.65    bluish green                              Example 12                                                                             6.0       120      0.9     blue                                      Example 13                                                                             8.0       110      0.62    blue                                      ______________________________________                                    

Reference Example 1

An initial DC voltage of 6.94 V was applied to the device as obtained inExample 11 to make the device continuously emit light under a constantcurrent condition. The brightness after 200 hours of continuous drivingmaintained 85% of the initial brightness, thus exhibiting an extremelystable light emission. The increase in the driving voltage was only one(1) V.

On the other hand, the device as obtained in Comparative Example 1 wasmade to continuously emit light under the condition same as above withthe result that the brightness after 200 hours of continuous drivingdecreased to one half, that is, 50% of the initial brightness.

EXAMPLES 14 TO 16

The procedures in Examples 1 to 8 were repeated to prepare the devicesexcept that for the positive hole injecting layer, CuPc (laminateconstitution of copper phthalocyanine/NPD with a film thickness of 20nm/40 nm) was used in Example 14, and MTDATA/NPD with a film thicknessof 60 nm/20 nm which is a kind of semiconductor oligomer was used inExamples 15 and 16. NPD:[N,N-bis(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine]##STR37##

A voltage of 7 V was applied to the device thus obtained, andmeasurements were made of the current density and the brightness of thedevice to calculate luminous efficiency of the same. The results aregiven in Table 4.

The charge injection auxiliary material as used in any of Examples 14 to16 functioned as the fluorescent dopant and had an energy gap less thanthat in the light emitting layer. The energy gap in a light emittinglayer is determined by the energy value at the light absorption end ofthe vapor-deposited film, while that in a charge injection auxiliarymaterial is determined by the energy value at the light absorption edgeof a dilute solution from a solvent having a low dielectric constant(for example, toluene and a halogenous solvent).

                  TABLE 4                                                         ______________________________________                                                                          (D)                                                                           Mixing                                                     (B)      (C)       ratio (%                                           (A)     (nm/sec) (nm/sec)  by weight)                                  ______________________________________                                        Example 14                                                                             DPAVBi    2.7˜3.0                                                                          0.12    3.8˜4.2                             Example 15                                                                             DPAVTP    2.5˜3.0                                                                          0.09    2.9˜3.4                             Example 16                                                                             DPAVB     3.0˜5.0                                                                          0.09    1.8˜2.9                             ______________________________________                                               Current Bright-  Luminous                                                     density ness     efficiency                                                                              Luminous                                           (mA/cm.sup.2)                                                                         (cd/m.sup.2)                                                                           (lm/W)    color                                       ______________________________________                                        Example 14                                                                             21.6      540      1.3     greenish blue                             Example 15                                                                             7.1       111      0.64    blue                                      Example 16                                                                             2.58      160      2.8     bluish green                              ______________________________________                                    

Remark: The abbreviated compound (A) are detailed as follows DPAVBi,DPAVB; as previously defined. ##STR38##

As can be seen from Table 4 and as compared with Comparative Example 1,any of the devices in these examples attains improvement in chargeinjection properties, decrease in voltage required to be applied andenhancement in efficiency.

EXAMPLES 17 AND 18

To any of the devices as obtained in Examples 14 and 15, an initialvoltage as shown in Table 5 was applied in an atmosphere of dry nitrogento carry out continuous driving under a constant current condition. As aresult, half-lives as shown in Table 5 were obtained, thus achievingprolonged service life. The prolonged service life is observed in acharge injection auxiliary material having in particular, an energy gapless than that in the light emitting layer. Table 5 gives the energy gapalong with the ionization energy in the charge injection auxiliarymaterial. The initial brightness was 100 cd/m², and the light emittinglayer had an energy gap of 2.97 eV.

                  TABLE 5                                                         ______________________________________                                                  Voltage                                                                       on            Charge injection                                      Initial     reduction                                                                              Half   auxiliary material                                voltage     to half  life   Energy gap                                                                            Ionization                                (V)         (V)      (hr)   (eV)    energy (eV)                               ______________________________________                                        Example 17                                                                            6.2     7.8      1000 2.84    5.6                                     Example 18                                                                            7.1     9.0       610 2.87    5.6                                     ______________________________________                                    

As can be seen from Table 5, the devices are low in voltage increase.The conventional devices usually bring about an increase in drivingvoltage of 3 to 4 V with the lapse of time, whereas the devices inExamples 17 and 18 showed a lessened increase in driving voltage of 1.6V and 1.9 V, respectively, thereby demonstrating excellent stability.

INDUSTRIAL AVAILABILITY

The charge injection auxiliary material according to the presentinvention is capable of effectively enhancing charge injectionproperties and hence is well suited for use in various organicelectronic devices such as electrophotographic photoreceptors andorganic EL devices.

In addition, the organic EL device comprising the above-mentioned chargeinjection auxiliary material according to the present invention ischaracterized by a lowered applied-voltage, an enhanced light emissionefficiency and a prolonged service life.

We claim:
 1. A functional layer of an organic electron device, saidfunctional layer comprising a positive-hole transporting organicsubstance which is subjected to a positive-hole injection from anexternal layer and has enhanced positive-hole injection properties byincorporation of a charge injection auxiliary material in saidfunctional layer, said charge injection auxiliary material comprising astilbene, distyrylarylene or tris(styrylarylene) compound, said chargeinjection auxiliary material being in an amount of 0.05 to 9% by weightbased on the weight of the positive-hole transporting organic substance.2. The functional layer according to claim 1, wherein the functionallayer is a light emitting layer, a positive-hole injecting layer, apositive-hole transporting layer or an electron barrier layer.
 3. Thefunctional layer according to claim 2, wherein the derivative ofstilbene, distyrylarylene or tris(styrylarylene) has at least oneelectron donating group.
 4. The functional layer according to claim 3,wherein the electron donating group is selected from the groupconsisting of an alkyl group having 1 to 10 carbon atoms, an aryloxygroup having 6 to 20 carbon atoms and an amino group with a hydrocarbonradical having 1 to 30 carbon atoms.
 5. The functional layer accordingto claim 1, wherein the charge injection auxiliary material comprises astilbene derivative of the formula (I) or (II) ##STR39## wherein Ar¹ isan aryl group having 6 to 20 carbon atoms, a thienyl group or abithienyl group,R¹ to R⁴ are each a hydrogen atom, an aryl group having6 to 20 carbon atoms, a thienyl group or a bithienyl group, R¹ and R²are each the same or different, R³ and R⁴ are each the same ordifferent, D¹ to D³ are each an aryl group having 6 to 20 carbon atomswhich is substituted with an electron donating group, a thienyl group ora bithienyl group or a condensed polycyclic group having 10 to 30 carbonatoms, D² and D³ are the same or different, and Ar¹ and R¹ to R⁴ areeach unsubstituted or substituted with an alkyl group having 1 to 10carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an aryloxygroup having 6 to 10 carbon atoms, an arylalkyl group having 7 to 10carbon atoms or an amino group with a hydrocarbon radical having 1 to 20carbon atoms.
 6. The functional layer according to claim 1 wherein thecharge injection auxiliary material comprises a distryrylarylenederivative of the formula (III) or (IV) ##STR40## wherein A² and Ar³ areeach an arylene group having 6 to 20 carbon atoms, a thienylene group ora bithienylene group,Ar⁴ is an aryl group having 6 to 20 carbon atoms, athienyl group or a bithienyl group, R⁵ to R¹² are each a hydrogen atom,an aryl group having 6 to 20 carbon atoms, a thienyl group or abithienyl group, R⁵ to R⁸ are the same or different; R⁹ to R¹² are eachthe same or different, D⁴ to D⁶ are each a thienyl group, a bithienylgroup, a condensed polycyclic group having 10 to 30 carbon atoms or anaryl group having 6 to 20 carbon atoms which is substituted with anelectron donating group, D⁴ and D⁵ are the same or different, and Ar² toAr⁴ and R⁵ to R¹² are each unsubstituted or substituted with an alkylgroup having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbonatoms, an aryloxy group having 6 to 10 carbon atoms, an arylalkyl grouphaving 7 to 10 carbon atoms or an amino group with a hydrocarbon radicalhaving 1 to 20 carbon atoms.
 7. The functional layer according to claim1 wherein the charge injection auxiliary material comprises atris(styrylarylene) derivative of the formula (V), (VI) or (VII)##STR41## wherein Ar⁵ to Ar⁷ are each a trivalent aromatic ring radicalhaving 6 to 24 carbon atoms,Ar⁸ to Ar¹⁰ are each an aryl group having 6to 20 carbon atoms, a thienyl group or a bithienyl group, Ar⁹ and Ar¹⁰are each the same or different, R¹³ to R³⁰ are each a hydrogen atom, anaryl group having 6 to 20 carbon atoms, a thienyl group or a bithienylgroup, R¹³ to R¹⁸ are each the same or different; R¹⁹ to R²⁴ are eachthe same or different; R²⁵ to R³⁰ are each the same or different; D⁷ toD¹² are each an aryl group having 6 to 20 carbon atoms which issubstituted with an electron donating group, a thienyl group or abithienyl group or a condensed polycyclic group having 10 to 30 carbonatoms, D⁷ to D⁹, D¹⁰ and D¹¹ are each the same or different, and Ar⁵ toAr¹⁰ and R¹³ to R³⁰ are each unsubstituted or substituted with an alkylgroup having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbonatoms, an aryloxy group having 6 to 10 carbon atoms, an arylalkyl grouphaving 7 to 10 carbon atoms or an amino group with a hydrocarbon radicalhaving 1 to 20 carbon atoms.
 8. An organic electroluminescence devicewhich comprises an anode, a cathode and disposed therebetween a lightemitting layer containing a charge injection auxiliary material, saidcharge injection auxiliary material having an ionization energy which issmaller than the ionization energy of said light emitting layer, saidcharge injection auxiliary material comprising a stilbene,distyrylarylene or tris(styrylarylene) derivative, said charge injectionauxiliary material being in an amount of 0.05 to 9% by weight based onthe weight of the light emitting layer.
 9. The organicelectroluminescence device according to claim 8, said charge injectionauxiliary material has an energy gap which is smaller than the energygap of the light emitting layer.
 10. The organic electroluminescencedevice according to claim 9, wherein the charge injection auxiliarymaterial is excited by the recombination of positive holes and electronsin the light emitting layer whereby light is emitted.
 11. The organicelectroluminescence device according to claim 9, wherein the chargeinjection auxiliary material has an energy gap which is smaller than theenergy gap of the light emitting layer by at least 0.1 eV.
 12. Thefunctional layer according to claim 3, wherein the electron donatinggroup is selected from the group consisting of phenoxy group,biphenyloxy group, naphthloxy group, anthranyloxy group, terphenylyloxygroup, methoxy group, ethoxy group, isopropoxy group, tert-butyloxygroup, pentyloxy group, dimethylamino group, diethylamino group,diphenylamino group, phenylmethylamino group, phenylethylamino group,phenylmethylethylamino group, ditolylamino group, ethylphenylaminogroup, phenylnaphthylamino group and phenylbiphenylylamino group. 13.The functional layer according to claim 1, wherein the charge injectionauxiliary material comprises a compound selected from the groupconsisting of ##STR42##
 14. The functional layer according to claim 1,wherein the charge injection auxiliary material comprises a compoundselected from the group consisting of ##STR43##
 15. The organicelectroluminescence device according to claim 8, wherein the chargeinjection auxiliary material is contained in an amount of 0.5 to 5% byweight of the light emitting material.
 16. The organicelectroluminescence device according to claim 15, wherein the chargeinjection auxiliary material comprises a compound ##STR44##
 17. Theorganic electroluminescence device according to claim 15, wherein thecharge injection auxiliary material comprises a compound ##STR45##
 18. Afunctional layer of an organic electron device, said functional layercomprising a positive-hole transporting organic substance which issubjected to a positive-hole injection from an external layer and hasenhanced positive-hole injection properties by incorporation of a chargeinjection auxiliary material in said functional layer, said chargeinjection auxiliary material comprising a distyrylarylene ortris(styrylarylene) compound, said charge injection auxiliary materialbeing in an amount of 0.05 to 9% by weight based on the weight of thepositive-hole transporting organic substance.